Make the camera go and return on the path?
You can achieve this using the following steps:


Create a path with the desired shape
Switch to Edit Mode, select all control points and duplicate them Shift + D and unselect all
Border select the point were the Camera is supposed to turn around
Create a segment between the two select control points by pressing F
Add a Follow Path modifier to the camera, tick the Follow Curve checkbox
Press the Animate Path button in the modifier


With the two points being in the same place the camera turn will be very sudden, but I assume this is what you want, judging by your description.